1. Field of the Invention
The present invention relates generally to an apparatus and method for receiving data in a mobile communication system using an Adaptive Antenna Array (AAA) scheme, and in particular, to an apparatus and method for receiving data using an adaptive reception beam weight generation scheme.
2. Description of the Related Art
A “next generation mobile communication system” has evolved into a packet service communication system that transmits burst packet data to a plurality of mobile stations (MSs). The packet service communication system is designed to transmit mass data. Such a packet service communication system has been developing for high-speed packet service. In this regard, the 3rd Generation Partnership Project (3GPP), a standardization organization for an asynchronous communication scheme, proposes a High Speed Downlink Packet Access (HSDPA) to provide the high-speed packet service, while the 3rd Generation Partnership Project 2 (3GPP2), a standardization organization for a synchronous communication scheme, proposes a 1× Evolution Data Only/Voice (1× EV-DO/V) to provide the high-speed packet service. Both the HSDPA and the 1× EV-DO/V intend to provide high-speed packet service for smooth transmission of Web/Internet service, and in order to provide the high-speed packet service, a peak throughput and average throughput should be optimized for smooth transmission of the packet data as well as the circuit data, e.g., voice service data.
In order to support the high-speed transmission of packet data, a communication system employing the HSDPA (hereinafter referred to as an “HSDPA communication system”) has newly introduced 3 kinds of data transmission schemes: an Adaptive Modulation and Coding (AMC) scheme; a Hybrid Automatic Retransmission Request (HARQ) scheme; and a Fast Cell Selection (FCS) scheme. The HSDPA communication system increases a data rate using the AMC, HARQ, and FCS schemes.
A communication system using the 1× EV-DO/V (hereinafter referred to as a “1× EV-DO/V communication system”) is another communication system for increasing a data rate. The 1× EV-DO/V communication system also increases a data rate to secure system performance. Aside from the new schemes such as AMC, HARQ and FCS, there is a Multiple Antenna scheme, which is another scheme for coping with the limitation in assigned bandwidth, i.e., increasing a data rate. The Multiple Antenna scheme can overcome the limitation of bandwidth resource in a frequency domain because it utilizes a space domain.
A communication system is constructed such that a plurality of MSs communicate with each other via one base station (BS). When the BS performs a high-speed data transmission to the MSs, a fading phenomenon occurs due to a characteristic of radio channels. In order to overcome the fading phenomenon, a Transmit Antenna Diversity scheme, which is a kind of the Multiple Antenna scheme, has been proposed. The Transmit Antenna Diversity scheme transmits signals using at least two transmission antennas to minimize a loss of transmission data due to the fading phenomenon, thereby increasing a data rate.
Generally, in a wireless channel environment in a mobile communication system, unlike in a wired channel environment, a transmission signal is actually distorted due to several factors, such as multipath interference, shadowing, wave attenuation, time-varying noise, interference, etc. Fading caused by the multipath interference is closely related to the mobility of a reflector or a user (or aMS), and actually, a mixture of a transmission signal and an interference signal is received. Therefore, the received signal suffers from severe distortion during its actual transmission, thereby reducing performance of the entire mobile communication system. The fading may result in the distortion in the amplitude and the phase of the received signal, preventing high-speed data communication in the wireless channel environment. Many studies are being conducted in order to resolve the fading. Accordingly, in order to transmit data at a high speed, the mobile communication system must minimize a loss caused by a characteristic of a mobile communication channel, such as fading, and interference of an individual user. A diversity scheme is used to prevent unstable communication due to the fading, and multiple antennas are used to implement a Space Diversity scheme.
Transmit Antenna Diversity is popularly used as a scheme for efficiently resolving the fading phenomenon. The Transmit Antenna Diversity scheme receives a plurality of transmission signals that have experienced an independent fading phenomena in a wireless channel environment, thereby coping with distortion caused by the fading. The Transmit Antenna Diversity is classified into Time Diversity, Frequency Diversity, Multipath Diversity, and Space Diversity. In other words, a mobile communication system must cope well with the fading phenomenon that severely affects communication performance, in order to perform the high-speed data communication.
As indicated above, the fading phenomenon must be overcome because it reduces the amplitude of a received signal up to several dB to tens of dB. For example, a Code Division Multiple Access (CDMA) scheme utilizes a Rake receiver that can achieve diversity performance using a delay spread of the channel. The Rake receiver is a kind of a Receive Diversity scheme for receiving multipath signals. However, the Receive Diversity used in the Rake receiver is disadvantageous in that it cannot achieve a desired diversity gain when the delay spread of the channel is relatively small.
The Time Diversity scheme efficiently copes with burst errors occurring in a wireless channel environment using interleaving and coding, and is generally used in a Doppler spread channel. Disadvantageously, however, the Time Diversity does not work well in a low-speed Doppler spread channel.
The Space Diversity scheme is generally used in a channel with a low delay spread such as an indoor channel and a pedestrian channel, which is a low-speed Doppler spread channel. The Space Diversity scheme achieves a diversity gain using at least two antennas. In this scheme, when a signal transmitted via one antenna is attenuated due to fading, a signal transmitted via another antenna is received, thereby acquiring a diversity gain. The Space Diversity is classified into Receive Antenna Diversity using a plurality of reception antennas and Transmit Antenna Diversity using a plurality of transmission antennas.
In the Receive-Adaptive Antenna Array (Rx-AAA) scheme, by calculating a scalar product of an appropriate reception beam weight vector and a signal vector of a reception signal received via an antenna array comprised of a plurality of reception antennas, a signal received in a direction desired by a receiver is maximized and a signal received in a direction not desired by the receiver is minimized. Herein, the reception beam weight represents a weight for generating the reception beam generated by the receiver in applying the Rx-AAA scheme. As a result, the Rx-AAA scheme amplifies only a desired reception signal to a maximum level, thereby maintaining a high-quality call and increasing the entire system capacity and service coverage.
Although the Rx-AAA scheme can be applied to both a Frequency Division Multiple Access (FDMA) mobile communication system and a Time Division Multiple Access (TDMA) mobile communication system, it will be assumed herein that the Rx-AAA scheme is applied to a communication system using CDMA schemes (hereinafter referred to as a “CDMA communication system”).
FIG. 1 is a block diagram illustrating a structure of a BS receiver in a conventional CDMA mobile communication system. Referring to FIG. 1, the BS receiver is comprised of N reception antennas (Rx_ANT) including a first reception antenna 111, a second reception antenna 121, . . . , and an Nth reception antenna 131, N radio frequency (RF) processors including a first RF processor 112, a second RF processor 122, . . . , and an Nth RF processor 132, being mapped to the corresponding reception antennas, N multipath searchers including a first multipath searcher 113, a second multipath searcher 123, . . . , and an Nth multipath searcher 133, being coupled to the corresponding RF processors, L fingers including a first finger 140-1, a second finger 140-2, . . . , and an Lth finger 140-L, for processing L multipath signals searched by the multipath searchers, a multipath combiner 150 for combining multipath signals output from the L fingers, a deinterleaver 160, and a decoder 170.
Signals transmitted by transmitters in a plurality of MSs are received at the N reception antennas over a multipath fading radio channel. The first reception antenna 111 outputs the received signal to the first RF processor 112. Each of the RF processors—includes an amplifier, a frequency converter, a filter, and an analog-to-digital (A/D) converter, and processes an RF signal. The first RF processor 112 RF-processes a signal output from the first reception antenna 111 to convert the signal into a baseband digital signal, and outputs the baseband digital signal to the first multipath searcher 113. The first multipath searcher 113 separates L multipath components from a signal output from the first RF processor 112. The separated L multipath components are output to the first finger 140-1 to the Lth finger 140-L, respectively.
The first finger 140-1 to the Lth finger 140-L, being mapped to the L multiple paths on a one-to-one basis, process the L multipath components. Because the L multiple paths are considered for each of the signals received via the N reception antennas, signal processing must be performed on N×L signals, and among the N×L signals, signals on the same path are output to the same finger.
Similarly, the second reception antenna 121 outputs the received signal to the second RF processor 122. The second RF processor 122 RF-processes a signal output from the second reception antenna 121 to convert the signal into a baseband digital signal, and outputs the baseband digital signal to the second multipath searcher 123. The second multipath searcher 123 separates L multipath components from a signal output from the second RF processor 122, and the separated L multipath components are output to the first finger 140-1 to the Lth finger 140-L, respectively.
In this same manner, the Nth reception antenna 131 outputs the received signal to the Nth RF processor 132. The Nth RF processor 132 RF-processes a signal output from the Nth reception antenna 131 to convert the signal into a baseband digital signal, and outputs the baseband digital signal to the Nth multipath searcher 133. The Nth multipath searcher 133 separates L multipath components from a signal output from the Nth RF processor 132, and the separated L multipath components are output to the first finger 140-1 to the Lth finger 140-L, respectively.
Accordingly, among the L multipath signals for the signals received via the N reception antennas, the same multipath signals are input to the same fingers. For example, first multipath signals from the first reception antenna 111 to the Nth reception antenna 131 are input to the first finger 140-1. In the same manner, Lth multipath signals from the first reception antenna 111 to the Nth reception antenna 131 are input to the Lth finger 140-L. The first finger 140-1 to the Lth finger 140-L are different only in signals input thereto and output therefrom, and are identical in structure and operation. Therefore, only the first finger 140-1 will be described for simplicity.
The first finger 140-1 has N despreaders including a first despreader 141, a second despreader 142, . . . , and an Nth despreader 143, being mapped to the N multipath searchers, a signal processor 144 for calculating a weight vector for generating a reception beam using signals received from the N despreaders, and a reception beam generator 145 for generating a reception beam using the weight vector calculated by the signal processor 144.
A first multipath signal output from the first multipath searcher 113 is input to the first despreader 141. The first despreader 141 despreads the first multipath signal output from the first multipath searcher 113 with a predetermined despreading code, and outputs the despread multipath signal to the signal processor 144 and the reception beam generator 145. Here, the despreading process is called “temporal processing.” Similarly, a first multipath signal output from the second multipath searcher 123 is input to the second despreader 142. The second despreader 142 despreads the first multipath signal output from the second multipath searcher 123 with a predetermined despreading code, and outputs the despread multipath signal to the signal processor 144 and the reception beam generator 145. Similarly, a first multipath signal output from the Nth multipath searcher 133 is input to the Nth despreader 143. The Nth despreader 143 despreads the first multipath signal output from the Nth multipath searcher 133 with a predetermined despreading code, and outputs the despread multipath signal to the signal processor 144 and the reception beam generator 145.
The signal processor 144 receives the signals output from the first despreader 141 to the Nth despreader 143, and calculates a reception beam weight set Wk for generating a reception beam. A set of first multipath signals output from the first multipath searcher 113 to the Nth multipath searcher 133 will be defined as “Xk.” The first multipath signal set Xk represents a set of first multipath signals received via the first reception antenna 111 to the Nth reception antenna 131 at a kth point, and the first multipath signals constituting the first multipath signal set Xk are all vector signals. The reception beam weight set Wk represents a set of reception beam weights to be applied to the first multipath signals received via the first reception antenna 111 to the Nth reception antenna 131 at the kth point, and the reception beam weights constituting the weight set Wk are all vector signals.
A set of signals determined by despreading all of the first multipath signals in the first multipath signal set Xk will be defined as yk. The despread signal set yk of the first multipath signals represents a set of signals determined by despreading the first multipath signals received via the first reception antenna 111 to the Nth reception antenna 131 at the kth point, and the despread signals constituting despread signal set yk of the first multipath signals are all vector signals. Herein, for the convenience of explanation, the term “set” will be omitted, and the underlined parameters represent sets of corresponding elements.
Each of the first despreaders 141 to the Nth despreaders 143 despreads the first multipath signal Xk with a predetermined despreading code, such that the reception power of a desired reception signal is greater than the reception power of an interference signal by a process gain. The despreading code is identical to the spreading code used in the transmitters of the MSs.
As described above, the despread signal yk of the first multipath signal Xk is input to the signal processor 144. The signal processor 144 calculates a reception beam weight Wk with the despread signal yk of the first multipath signal Xk, and outputs the reception beam weight Wk to the reception beam generator 145. As a result, the signal processor 144 calculates the reception beam weight Wk including a total of N weight vectors applied to the first multipath signal Xk output from the first reception antenna 111 to the Nth reception antenna 131, with the despread signals yk of a total of N first multipath signals output from the first reception antenna 111 to the Nth reception antenna 131. The reception beam generator 145 receives the despread signals yk of a total of the N first multipath signals Xk and a total of the N reception beam weight vectors Wk. The reception beam generator 145 generates a reception beam with a total of the N reception beam weight vectors Wk, calculates a scalar product of the despread signal yk of the first multipath signal Xk and the reception beam weight Wk corresponding to the reception beam, and outputs the result as an output zk of the first finger 140-1. The output zk of the first finger 140-1 can be expressed as shown in Equation (1).zk=wkHyk  (1)
In Equation (1), H denotes a Hermitian operator, i.e., a conjugate-transpose. A set zk of output signals zk from L fingers in the BS receiver is finally input to the multipath combiner 150.
Although only the first finger 140-1 has been described, the other fingers, the second finger 140-2 to the Lth finger 140-L, are to the same as the first finger 140-1 in operation.
The multipath combiner 150 combines the signals output from the first finger 140-1 to the Lth finger 140-L, and outputs the combined signal to the deinterleaver 160. The deinterleaver 160 deinterleaves the signal output from the multipath combiner 150 in a deinterleaving method corresponding to the interleaving method used in the transmitter, and outputs the deinterleaved signal to the decoder 170. The decoder 170 decodes the signal output from the deinterleaver 160 in a decoding method corresponding to the encoding method used in the transmitter, and outputs the decoded signal as final reception data.
The signal processor 144 calculates a reception beam weight Wk such that a Mean Square Error (MSE) of a signal received from a MS transmitter, desired to be received by a predetermined algorithm, becomes minimized. The reception beam generator 145 generates a reception beam using the reception beam weight Wk generated by the signal processor 144. The process of generating a reception beam such that the MSE is minimized is called “spatial processing.” When the Rx-AAA scheme is used in a CDMA mobile communication system, temporal processing and spatial processing are simultaneously performed. The operation of simultaneously performing temporal processing and spatial processing is called “spatial-temporal processing.”
The signal processor 144 receives multipath signals despread for each finger in the above-described manner, and calculates a reception beam weight capable of maximizing a gain of the Rx-AAA scheme according to a predetermined algorithm. The signal processor 144 minimizes the MSE.
Currently, a great deal of research is being conducted on a reception beam weight calculation algorithm for adaptively minimizing the MSE. However, the reception beam weight calculation algorithm for adaptively minimizing the MSE is an algorithm for reducing errors on the basis of a reference signal, and this algorithm supports a Constant Modulus (CM) scheme and a Decision-Directed (DD) scheme as a blind scheme, when there is no reference signal.
Further, the algorithm for reducing errors on the basis of a reference signal has trouble converging into a minimum MSE value desired by the system in an environment where a channel such as a fast fading channel suffers from a rapid change, or an environment where a high-order modulation scheme such as 16-ary quadrature amplitude modulation (16 QAM) is used. Even though it converges into a particular MSE value, the minimum MSE value is set to a relatively large value. When the minimum MSE value is set to a relatively large value, a gain that occurs from using the Rx-AAA scheme is reduced. Therefore, this algorithm is not suitable for a high-speed data communication system.